In general, when diesel fuel is burned in an engine, nitrogen oxides are produced in the exhaust gas. An EGR cooler provides a cooled dilutent to lower combustion temperatures and reduce the concentration of nitrogen oxides in the exhaust gases. Typically, when an engine is first started, a bypass valve, separate from the EGR cooler, is used to bypass the EGR cooler and redirect uncooled gasses through the engine to accelerate engine warmup. These bypass valves must withstand high temperature and are typically complicated, with an expensive, machined housing.
There is a need to provide an inexpensive and replaceable bypass valve for a EGR cooler.